DESCRIPTION (Verbatim from the Principal Investigator's abstract): The ability to detect and identify single nucleotide polymorphisms (SNP's) will become increasingly important in diagnosing human disease and disease tendencies, and cataloguing human genetic variations over the coming decade. Point mutations are among the most common SNP's found in oncogenic mutations associated with cancer. The research proposed here is aimed at study of a conceptually new approach to identification of SNP's, both in vitro and in intact tissues. The approach involves the use of novel chemistry for autoligation of short DNA probes, combined with competition between multiple probes for targets of interest. This is expected to yield SNP information with a very simple color-based readout. The specific aims of the work include testing of sequence specificity, increasing the generality of the autoligation chemistry, examination of methods for increasing rate and turnover, and testing in multiple formats, including cultured cells and tumor specimens. If successful, the methods will allow the discrimination of single-base mutations in oncogenes simply by examining cells under a microscope. Over the long term, it is hoped that this approach will give rise to clinically useful methods for the early diagnosis of cancer.